The present invention relates to an electric-control-type throttle valve apparatus for controlling the amount of intake air in an internal combustion engine.
Japanese Patent Publication 177534/1996 discloses a throttle valve control apparatus including a throttle valve body, a throttle valve installed in the air intake path of the throttle valve body via a rotatable shaft, an actuator for driving the throttle valve via a plurality of gears, and a detection means for detecting the rotation angle of the throttle valve.
The plurality of gears of this apparatus is composed of a first gear fixed to the shaft of the throttle valve, a third gear fixed to the rotation shaft of the motor used as the actuator, and a second gear engaged between the first and third gears. This gear arrangement can increase the speed reducing ratio, which can allow for fine control of the opening of the throttle valve.
Although the opening of the throttle valve can be finely controlled by obtaining a large gear ratio in the above-mentioned conventional throttle valve apparatus, it is not stated in the above-referenced publication how to determine the characteristics of the motor, or the gear ratio with which the torque of the motor is transmitted to the throttle valve, in order to realize a desired operation speed of the throttle valve.
In the above-described conventional apparatus, the throttle valve is opened or closed by a motor. If the opening or closing action of the throttle valve does not respond quickly to the motion of the acceleration pedal operated by a driver, the driver will notice the lag between the operations performed by the driver itself and changes in the operational state of the internal combustion engine. However, in an electric-control-type throttle valve apparatus, it is necessary to provide a force applying means for quickly returning the position of the throttle valve to a predetermined opening in the event of a problem which may affect fail-safe operation. Therefore, with such force applying means, the operation speed of the throttle valve cannot easily be increased, and so it is important to adequately determine the force applied from the force means, the performance of the motor, and the speed reducing ratio of the rotation speed of the motor relative to that of the throttle valve.
If this conventional throttle valve apparatus is applied to a direct injection engine in which fuel is directly injected in each cylinder, the following problems will likely occur.
In a conventionally used port injection engine in which fuel is injected into an air intake pipe, the engine is operated near the theoretical air to fuel ratio of 14.7. On the other hand, a direct injection engine is operated in a wide range of values of air to fuel ratio from 14.7 (theoretical ratio) to more than 40 (superlean ratio). Fuel burning near the theoretical air to fuel ratio is referred to as a uniform mixture charge burning state, and fuel burning at an air to fuel ratio higher than the theoretical ratio is referred to as a stratified charge burning state. It is easy to realize a stratified charge burning state in a direct injection engine because fuel is directly injected into a cylinder. FIG. 12 is a diagram showing the relationship between the fuel burning modes and operation states of an engine. The stratified charge burning mode is performed below an engine rotation speed of approximately 3000 rpm.
In implementing those burning modes, it is necessary to open the throttle valve wider in the stratified charge burning state than in the uniform mixture charge burning state. Therefore, when the operation of the engine is changed from the stratified charge burning state to the uniform mixture charge burning state, the throttle valve is driven in the valve closing direction. FIG. 4A and FIG. 4B show changes in time of the actuating amount of an acceleration pedal and changes in time of the opening of the throttle valve corresponding to the changes of the actuating amount of the acceleration pedal, respectively.
As shown in FIG. 4B, the throttle valve is widely opened in the stratified charge burning state, and it is driven initially in the valve closing direction when the operation of the engine is switched to the uniform mixture charge burning state. If the time necessary for the switching operation is long, the switching operation between the two burning states cannot be smoothly carried out, and the output power of the engine rapidly changes. Consequently, a shock caused by the switching operation is transmitted to the passengers and the driver of the vehicle, which degrades both the operationality of the vehicle and the comfort of riding in the vehicle.
On the other hand, if the throttle valve is driven at a high speed, it is also necessary to rotate the motor driving the throttle valve at a high speed. In such high speed operations, the higher the speed the motor is rotated at, the larger the counter-electromotive force for braking the rotation of the throttle valve becomes. Therefore, there may be a large current that is beyond the permitted value for the switching elements used in a drive circuit for driving the motor. It is then necessary to use switching elements with a higher permitted current value for the drive circuit of the motor. However, switching elements with the required larger permitted current cannot be always acquired. Even when switching elements with the required larger permitted current can be acquired, such elements are very expensive and are unsuitable for use in a vehicle. As another means for restricting the value of the current flowing in the drive circuit of the motor below the permitted current value, it is also possible to provide a current limiting circuit in the drive circuit. However, this tends to increase the production cost, and if the provided current limiting circuit breaks down, it is possible that the increased current cannot be kept below the permitted current value. Thus, such a solution does not offer a sufficient fail-safe function.
An object of the present invention is to realize a highly reliable electric-control-type throttle valve apparatus which is capable of performing standard opening and closing operations and offering a fail-safe function of securing the position of a throttle valve at which a vehicle can be safely driven at an appropriate operation speed even in the event of a failure of the motor which drives the throttle valve.
A first feature of the present invention designed to attain the above object is to provide an electric-control-type throttle valve apparatus including a motor, a speed reducing mechanism for reducing the rotation speed that is transmitted from the motor, a throttle valve connected to the speed reducing mechanism, and a force applying means for applying a force to the throttle valve towards returning the valve to its initial position, and means for adjusting the opening of the throttle valve by driving the motor; wherein the specification parameters of the motor, the speed reducing mechanism, and the force applying means are such that the operation time t from the minimum opening to the maximum opening of the throttle valve, which is determined by the following equation (1):                               t          =                                    π                                                (                                                                                    T                        max                                            ⁢                      N                                        -                                          T                      s                                                        )                                J                                                    ,                            (        1        )            
where
Tmax=KME/RM, TS: the preload of a return spring of the force applying means [Nm], Tmax: the torque of the motor [Nm], N: the speed reducing ratio, J: the equivalent moment of inertia [kgm2], Km: the torque constant [Nm/A], Rm: the impedance of the motor [xcexa9], and E: the voltage applied to the motor [V],
is shorter than a prescribed target operation time t*.
A second feature of the present invention resides in the fact that, in the above-described electric-control-type throttle valve apparatus, the target operation time t* is 80 ms.
A third feature of the present invention resides in the fact that, in the above-described electric-control-type throttle valve apparatus, the values of the specification parameters are those which occur at the temperature of 120xc2x0 C.
A fourth feature of the present invention resides in the fact that, in the above-described electric-control-type throttle valve apparatus, the applied voltage is approximately 13 V.
A fifth feature of the present invention resides in the fact that, in the above-described electric-control-type throttle valve apparatus, the torque constant Km is 0.035xc2x10.0035 Nm/A, the resistance of the motor Rm is 1.6xc2x10.1xcexa9, and the speed reducing ratio N is from 9.8 to 10.8, and is preferably 10.3 at a temperature of 20xc2x0 C.
A sixth feature of the present invention resides in the fact that, in the above-described electric-control-type throttle valve apparatus, the preload torque Ts of the return spring is from 0.3 to 0.4 Nm, and is preferably 0.35 Nm.
A seventh feature of the present invention resides in the fact that, in the above-described electric-control-type throttle valve apparatus, the torque constant Km is from 0.025 to 0.04 Nm/A, and is preferably from 0.03 to 0.037 Nm/A, and the resistance of the motor Rm is from 1.0 to 2.5xcexa9, and is preferably from 1.3 to 2.2xcexa9.
An eighth feature of the present invention resides in the fact that, in the above electric-control-type throttle valve apparatus, the specification parameters have values such that a differential coefficient of the operation time t expressed by the equation (1) with respect to the speed reducing ratio N is positive.
A ninth feature of the present invention resides in the fact that, in the above-described electric-control-type throttle valve apparatus, the speed reducing ratio N is from 9.8 to 10.8.
A tenth feature of the present invention resides in the fact that the above-described electric-control-type throttle valve apparatus further includes a detector for detecting the applied voltage E, a means for measuring the counter-electromotive force induced in the motor, and a control unit for controlling the motor, wherein the control unit predicts changes in a value obtained by dividing the sum of the detected applied voltage E and the measured counter-electromotive force by the impedance Rm of the motor, and controls the applied voltage so as not to permit current to flow beyond the maximum permitted current value in the circuit used for driving the motor.
An eleventh feature of the present invention is to provide an electric-control-type throttle valve apparatus including a motor, a speed reducing mechanism for reducing the rotation speed that is transmitted from the motor, a throttle valve connected to the speed reducing mechanism, and a force applying means for applying a force to the throttle valve towards returning the valve to its initial position, and means for adjusting the opening of the throttle valve by driving the motor; wherein the specification parameters of the motor, and the force applying means have values satisfying the following inequality (2):                                           R            m                     greater than                                     (                              E                +                                                      K                    e                                    ⁢                                      xe2x80x83                                    ⁢                                                            θ                      .                                        m                                                              )                                      I              lim                                      ,                            (        2        )            
where {dot over (xcex8)}={dot over (xcex8)}v, N, and Vm=K{dot over (xcex8)}m, and Rm is the resistance of the motor [xcexa9], E: the voltage applied to the motor [V], Ke: the induction voltage coefficient [V/rpm], {dot over (xcex8)}m: the rotation speed of the motor [rpm], {dot over (xcex8)}v: the rotation speed of the throttle valve [rpm], N: the speed reducing ratio, and Vm: the counter-electromotive force induced in the motor.
A twelfth feature of the present invention resides in the fact that, in the above-described electric-control-type throttle valve apparatus, the applied voltage E is approximately 13 V, and the motor impedance Rm is more than 1.2xcexa9 at 20xc2x0 C.
A thirteenth feature of the present invention resides in the fact that the above-described electric-control-type throttle valve apparatus further includes a detector for detecting the applied voltage E and a control unit for controlling the motor, wherein the control unit predicts changes in the value of the right-hand side of the inequality (2) and controls the applied voltage E so as to always satisfy the inequality (2).
A fourteenth feature of the present invention resides in the fact that, in the above-described electric-control-type throttle valve apparatus, the throttle valve apparatus is used in a direct-injection combustion engine.